Born in 1951, Bertha Lewis grew up in Philadelphia and attended Hanover College in Indiana during the late 1960s. In 1979 she moved to New York, where she initially worked as a customer-service representative for the telephone company and later produced off-Broadway plays. In 1983, Lewis and some friends moved into what had been advertised as a “low rent” building in the South Bronx and began refurbishing it while paying monthly rental fees to a man who falsely claimed to be the landlord. After two years, the city tried to oust Lewis and her companions as squatters when it found out that their “landlord” did not in fact own the building where they were living. In response, Lewis and the others formed a tenants' association (with Lewis as spokeswoman) and, with the help of attorney William Kunstler, won a court ruling that allowed them to stay.

In 1986, Lewis was recruited by Banana Kelly, a Bronx community activist group, to help organize neighborhood residents in a variety of political and social initiatives. In 1991, Jon Kest, who headed the New York branch of the community organization ACORN, persuaded Lewis to serve as director of the ACORN Housing Corporation’s NYC Loan Counseling Program. There, Lewis helped to negotiate agreements forcing major banks to comply with the economically disastrous mandates of the Community Reinvestment Act, which ultimately helped bring about the infamous housing crisis of 2008. In 1994 Lewis became the head of New York ACORN and went on to hold that position for the next 14 years.

In 1998, Lewis co-founded the Working Families Party (WFP) and served for a number of years as its vice chairman. When WFP supported Hillary Clinton's successful U.S. Senate campaign in 2000, Lewis stated: “Candidates know that when they’re on our [WFP ballot] line, they’re committed to certain things […] Hillary knows that if she wins, we’re going to be knockin’ on her door. She won’t be able to hide.”

In May 2008, Lewis replaced Wade Rathkeas ACORN's national CEO and Chief Organizer. Initially, she focused her attention on organizing ACORN’s national get-out-the-vote campaign for Democraticpresidential nominee Barack Obama, who had longstanding, close ties to ACORN; Obama appointedLewis’s friend and former assistant at ACORN, Patrick Gaspard, as his presidential campaign's political director.

By October 2008, ACORN was under investigation for voter fraud in 13 states. Then, in September 2009, the independent journalist James O’Keefe released a series of explosive, hidden-camera videotapes showing ACORN employees discussing, with an undercover confederate, the feasibility of helping the confederate to obtain a federal loan for the purpose of financing a brothel staffed by underaged illegal aliens. Under a firestorm of criticism. Lewis initially sought to contain the controversy by firing all the employees who appeared in O’Keefe’s videos and characterizing them as nothing more than a handful of rogues. She also suggested that O’Keefe's investigation was a racist attempt to undermine the otherwise good work of “a black and brown organization.”

But Lewis could not halt the political repercussions of the videos. In July 2009, Rep. Darrell Issa filed a House report investigating ACORN as a criminal enterprise; in early September the Census Bureau severedall ties with the organization; and a few days after that, Congress voted to strip ACORN of federal funding. Lewis responded to these measures by championing previous “ACORN victories” and vowing that “nothing will be able to stop us from 40 more” years of activism.

In early 2010, Lewis continued to spin the scandal as a “series of well-orchestrated, relentless, well-funded right-wing attacks that are unprecedented since the McCarthy era.” But with various ACORN chapters splintering away from the national organization, Lewis finally announced that ACORN was folding, effective April 1.

After the bankruptcy and collapse of ACORN in 2010, Lewis founded the Black Institute, an organization whose mission is “to shape intellectual discourse ... and impact public policy uniquely from a Black perspective.”

During a March 25, 2010 speech to the Young Democratic Socialists, Lewis stated that “any group [like YDS] that says, ‘I’m young, I’m democratic, and I’m a socialist,’ is alright with me.” Alluding to what she perceived as the unjust persecution of her ACORN organization, she also lamented that “we are living in a time which is going to dwarf the McCarthy era … [and] dwarf the internments during World War II … [and] dwarf the era of Jim Crow and segregation.” Moreover, Lewis smeared the Tea Party Movementas a contemptible “bowel movement” filled with “racism.” And she explained that white people's opposition to a pro-amnesty, pro-open borders immigration policy was rooted in the fact that: (a) “the [white] fear of a black planet is real,” and (b) “we gettin’ ready to have a majority country [the U.S.] of people of color,” a phenomenon “that’s going to change our psyche and our economics.”

Lewis reprised this theme in a September 2012 addressto the annual political conference of the Congressional Black Caucus, where she urged African Americans to “get down with immigration reform” because an increased influx of nonwhites – e.g., “Latino cousins” and “Asian cousins” – to the U.S. “could change everything.”

Lewis played a key, behind-the-scenes role in the success of the 2013 Democratic mayoral primary campaign of Bill de Blasio in New York. Specifically, ACORN's local successor group, New York Communities for Change (NYCC), formally endorsed de Blasio; NYCC field director Harold Miller, a Lewis protege, helped run the de Blasio campaign's field operation; and Lewis herself stood behind de Blasio during his primary-night victory address on September 10.